Moment to moment regulation of arterial pressure in the conscious animal is mediated by neural reflexes. Of these reflexes, the artificial baroreceptor reflex is predominant. However, low pressure receptors can modulate the reflex control of pressure. Receptors in the heart, lungs, spleen, kidney and liver can all reflexly inhibit efferent sympathetic nerve activity. Several observations of baroreflex control from the basis for these studies. FIrst, arterial baroreceptor reset to changes in pressure of any magnitude. Secondly, the baroreflex (ie. pressure- sympathetic nerve activity relationship) only resets in the conscious rabbit if changes in pressure do not exceed 20 mmHg. If pressure changes exceed 20mmHg, the baroreflex does not reset. Thirdly, progressive, acute hypertension (above 20mmHg) progressively attenuates the baroreflex. This reduces the ability of the baroreflex to compensate for further changes in pressure. Lastly, cardiac receptors are tonically inhibitory to for further changes in pressure. Lastly, cardiac receptors are tonically inhibitory to sympathetic outflow, but are not responsible for this progressive attenuation. It has been suggested that pulmonary receptors play a role in baroreflex modulation since they inhibit sympathetic activity and the pulmonary bed becomes congested with acute hypertension. To date, baroreflex modulation in conscious animals has only been studied in normotensive animals. This study examines the role of cardiac and pulmonary receptors in both normotensive and hypertensive conscious rabbits. Rabbits will be prepared with aortic and caval occluders, intrapericardiac catheters and renal nerve recording electrodes. Some rabbits will also be prepared with aortic nerve electrodes. Baroreflex curves will be obtained in normotensive and chronically hypertensive conscious rabbits before and during progressive acute hypertension, following cardiac receptor blockade, and following will be compared to overall baroreflex resetting in normotensive and hypertensive rabbits by recording afferent aortic and efferent renal sympathetic nerve activity simultaneously. Lastly, the mechanical properties baroreceptive and capacitance vessels will be studied in response to physiological and pharmacological stimuli in normotensive and hypertensive rabbits. Information from these experiments will enhance our understanding of the integrated baroreflex control of arterial pressure in the conscious animal, and our understanding of chronic hypertension development on baroreflex modulation.